In conventional drying processes, water is removed as a vapor from the surfaces of fine metal powders, that is, powders having an average size of less than about 100 micrometers in diameter. (The powder is heated until the water boils away.) This technique is energy intensive because (1) water has a high heat of vaporization, (2) water tends to bond to the metal powder surfaces and (3) fine metal powders tend to have a high surface area.
It is necessary to remove the water thoroughly from the metal powder before the powder can be used in applications such as in plasma processing and rapid solidification processes. If even small amounts of water are allowed to remain on the powder, there is risk of degrading the chemistry of the powder by increasing the oxygen content of the powder. Also, residual water on metal powder particle surfaces, especially powders of fine particle size such as less than 10 micrometers in diameter, can promote pyrophoricity. Also residual water can also agglomerate the powder and make it stick together.
Therefore, a method to economically and thoroughly dry fine metal powders for subsequent processing, such as plasma melting and rapid solidification would be highly desirable.